taVNS Effects on Fear Ratings in Naturalistic Context

In a sham-controlled, participant-blinded, between-subjects design, 70 participants were randomly assigned to either active transcutaneous auricular vagus nerve stimulation (taVNS) or sham stimulation. The taVNS group received stimulation via a modified transcutaneous electrical acupoint stimulation device, with ear clip electrodes attached to the left cymba conchae to target vagus nerve branches. The sham group received identical electrode placement on the left earlobe, a non-vagus-innervated site. Stimulation intensity was individually calibrated to a perceptible but non-painful level to ensure vagal activation while maintaining participant comfort.

Upon arrival, all participants completed standardized mood and trait questionnaires. To assess emotional and physiological changes, two administrations of the Positive and Negative Affect Schedule (PANAS) and blood pressure/pulse measurements (pre- and post-intervention) were conducted. During the fear rating task, participants viewed a 600-second horror movie while continuously rating their subjective fear intensity (0-100 scale) every 0.51 seconds (1,170 total ratings). Functional near-infrared spectroscopy (fNIRS) data were simultaneously recorded using the NIRSIT LITE system to monitor cortical hemodynamic responses. Additionally, skin conductance responses were measured vy BIOPAC MP150 system.

Inclusion criteria

Healthy participants without color blindness, current or regular substance or medication use, any current or history of medical or psychiatric disorders and contraindications for MRI.

Exclusion criteria

• Color blindness,
• Current or regular substance or medication use
• any current or history of medical or psychiatric disorders and contraindications for MRI